After drilling for two decades through more than two miles of antarctic ice, Russian scientists are on the verge of entering a vast, dark lake that hasn’t been touched by light for more than 20 million years.

Scientists are enormously excited about what life-forms might be found there but are equally worried about contaminating the lake with drilling fluids and bacteria, and the potentially explosive “de-gassing” of a body of water that has especially high concentrations of oxygen and nitrogen.

To prevent a sudden release of gas, the Russian team will not push the drill far into the lake but just deep enough for a limited amount of water — or the slushy ice on the lake’s surface — to flow up the borehole, where it will then freeze.

Reaching Lake Vostok would represent the first direct contact with what scientists now know is a web of more than 200 subglacial lakes in Antarctica — some of which existed when the continent was connected to Australia and was much warmer. They stay liquid because of heat from the core of the planet.

“This is a huge moment for science and exploration, breaking through to this enormous lake that we didn’t even know existed until the 1990s,” said John Priscu, a researcher at Montana State University who has long been involved in antarctic research, including a study of Vostok ice cores.

“If it goes well, a breakthrough opens up a whole new chapter in our understanding of our planet and possibly moons in our solar system and planets far beyond,” he said. “If it doesn’t go well, it casts a pall over the whole effort to explore this wet underside of Antarctica.”

Priscu said Russian scientists on the scene e-mailed him last week to say they had stopped drilling about 40 feet from the expected waterline to measure the pressure levels deep below. Priscu said he expected that they were also sending down a special “hot water” drill to make the final push, but a message from the Russian team Monday reported “no news.”

If the Russians break through as planned within the next week, it will cap more than 50 years of research in what are considered the harshest conditions in the world — where the surface temperatures drop to 100 degrees below zero. That extreme cold is likely to return within a few weeks, at the end of the antarctic summer, putting pressure on the Russians to make the final push or pull out until the next antarctic drilling season, starting in December.

The extreme cold, which limited drilling time, contributed to the long duration of the project. The Russian team also ran into delays caused by financial strains and by efforts to address international worries about their drilling operation.

Valery Lukin, who is leading the effort for the Russians, is on the ice. Last year, he told Reuters that their work is “like exploring an alien planet where no one has been before. We don’t know what we’ll find.”

The ‘crown jewel’

American and English teams are planning drilling campaigns next year into much smaller antarctic lakes as scientists work to understand the dynamics of the continent, which holds more than 70 percent of the world’s fresh water. But Vostok — where the former Soviet Union began work after the United States settled in at the South Pole more than 50 years ago — is now acknowledged to be the “crown jewel” of Antarctica from a scientific perspective.

In recent years, researchers have discovered that microbes live in the ice wherever they explore in Antarctica, including deep in the Vostok borehole. This finding has revolutionized thinking about the snow- and ice-covered continent and has encouraged researchers, including Priscu, to conclude that life almost certainly will be found in Vostok and the other subglacial lakes.

If microbes are found in Vostok, the discovery would have particular significance for astrobiology, the search for life beyond Earth. That’s because Jupiter’s moon Europa and Saturn’s moon Enceladus have deep ice crusts that scientists think cover large amounts of liquid water warmed by sources other than the sun — just like Vostok.

Because of the stakes involved, the Russian effort has drawn criticism for its extensive use of kerosene, Freon and other chemicals to enable the drilling and to keep the borehole open during the long winter. Priscu said the Russians have worked with an international group he helped form to come up with cleaner ways to drill the final section of the hole.

Organizations including the Antarctic and Southern Ocean Coalition, which is the official environmental umbrella group sitting at Antarctic Treaty organization meetings, have spoken against the drilling methods used by the Russians. Some other groups have called for a ban on scientific research beneath the antarctic ice sheet so the area can remain pristine.

Claire Christian, director of the coalition’s secretariat, said her group generally supports study of the subglacial antarctic lakes but wishes that the first entry would not take place at Vostok because of its importance. Of the Russian team, she said, “They have responded to some concerns but are not drilling to the highest standards available.” The Russian team could not be reached for comment.

Researchers such as Robin Bell, of the Lamont-Doherty Earth Observatory at Columbia University, said learning more about the subglacial world in Antarctica is essential to understanding the changing climate and how it may effect Earth. Because the continent has so much of the world’s freshwater ice, significant changes there would have a major impact on sea-level rise.

Bell, who has studied Vostok using satellite imaging and other above-surface instruments, said the lake is part of a complex system in which ice sheets bring in meltwater at their bottoms and later carry refrozen water elsewhere. She said that although the lake has not “felt the wind” in 20 million to 30 million years, the water in it is not as ancient — in the 100,000s to low millions of years old. The only ancient water present, she said, is probably in the sediment at the bottom.

She, too, has concerns about contamination and equipment failures but said the Russians see their Vostok work as a high-profile symbol of scientific exploration and prowess and so are taking extra care.

Danger of giant geyser

Vostok, which is about the size of New Jersey, is the world’s third-largest lake by volume of water. Priscu said the gas in the lake makes it like a can of carbonated soda: Open it under high pressure, and it will spurt out.

He said the doomsday scenario for the Russian breakthrough would be if the suddenly released water pushed its way past machinery to block it and shot up the borehole, which is six to eight inches in diameter at the top. The result, he said, could be an enormous geyser that could empty a quarter of the lake. Priscu said he didn’t expect that to happen, but if it did, the sudden addition of substantial water vapor to the antarctic atmosphere could change the continent’s weather in unpredictable ways.

Some American Antarctica specialists think the combination of the Russian technique and the fact that the team is sampling from the “top” of the subterranean lake means that its chances of finding microbes is lower than if it went deeper into the water. Priscu and his former student Brent Christner, now a professor at Louisiana State University, published a paper in 2006 describing a variety of microbes in a Vostok ice core sample, but the Russian team has generally written off the microbes found as contamination.

American researchers will begin drilling into the Whillans Ice Stream in western Antarctica late this year, and the British will drill into the much deeper Lake Ellsworth, also in western Antarctica. Both are using techniques more consistent with best drilling practices than the Russians are doing at Vostok and are better equipped to find microbial life.

“Hopefully, all three projects will succeed, and then we’ll enter a new era of science and maybe cooperation,” Priscu said. “I could imagine an international team going back to Vostok and starting a project to drill much further into the lake with a higher level of technology and innovation.”

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